Process of manufacturing plywood



0. L'. SPONSLER M, E. DUNLA P AND s. B. HENNING. PROCESSOFWMANUFACTURING PLYWOOD. APPLICATION FILED JUNE l9, 191s.

veniors O\en us L. Sponsler TlaTThcw E. Dunlap fiherbu rne E .Hcnni m2UNITED STATES PATENT OFFICE.

OLilNUS I1. SPONSLER, MATTHEW E. DUNLAP, AND SHERBURNE B. HENNING, OFMADISON, WISCONSIN, ASSIGNORS TO THE UNITED STATES OF AMERIGA.

PROCESS OF MANUFACTURING PLYWOOD.

Specification of Letters Patent.

Patented Apr. 6, 1920.

Application filed June 19, 1918. Serial No. 246,859.

To all whom it may concern:

Be it known that we, OLENUS L. SPONSLER, MATTHEW E. DUNLAP, andSHERBURNE B. HENNING, citizens of the United States,- residing atMadison, in the county of Dane.

and State of Wisconsin, have invented a new and useful Improvement inProcesses of Manufacturing Plywood, of which the following is aspecification.

, Our invention relates to the method of manufacturing a waterproofplywood with dry glue and has for its object the production of a plywoodwhich is waterproof, light, strong, flexible, and tough, and which iscapable of receiving a fireproof and waterproof coating. Our method ofproducing plywood prevents wrinkling, checking and overlapping, andresults in a plywood which will not warp after it has been pressed. A.plywood prepared in accordance with our invention is adapted for use assurface coverings and especially as wing and fuselage coverings ofairplanes.

Our invention avoids the difficulties attendant upon the use of wet gluesuch as the handling of the wood while wet. Wrinkling in the core and onthe faces of plywood is usually due to swelling of the plies as a resultof their absorption of moisture from Wet glues. Checking and warping aredue to the same cause. Our use of #dry glue eliminates the water whichis a constituent of wet glue and thus overcomes the usual defects in theproduction of plywood.

Wet glues normally pass through very thin plies and are apt to stick tothe separating cauls if cold pressed, and to the press plates if hotpressed. This objection is overcome by the use of dry glue, which doesnot soften enough to pass through the face plies.

In the accompanying drawing, Figure 1 is an illustration of the generalform of the plies and glue sheet.

Fig. 2, shows the plies and glue sheets between the platens of theconventional hot press, the parts only of the platens next to the sheetsbeing shown.

In carrying out our invention, the glue to be used is prepared asfollows: To twenty parts of blood albumin (black soluble) is addedthirty to eighty parts of water by weight. This mixture is allowed tosoak for about two hours, without stirring. It is then thoroughlystirred-and strained through a thirty to forty mesh screen. There is nowadded to this mixture fifteen to forty parts by weight of a sugar syrup,such for example as corn syrup, the purpose of this syrup being toretain a greater per cent. of moisture than would otherwise be retainedwhen the mixture has dried. WVhile we have found that a sugar syrup maybe advantageously used to retain the moisture to be released under theheat and pressure to be specified, we do not limit ourselves to thiscompound as other compounds may be used for the same purpose.

Thin plies of wood, sheets of paper, or fabric are then dipped or passedthrough this glue solution to become thoroughly covered and areafterward dried. These adhesive sheets may be stacked in piles or rolledfor further use.

In manufacturing plywood, these sheets are placed between the plies,alternating with them. The plies and adhesive sheets are then subjected,between hot plates with or without cauls, to a pressure of about fiftyto one hundred fifty pounds per square inch while the press is kept at atemperature approximately between two hundred and two hundred twentydegrees Fahrenheit. Good results are obtained by continuing said heatand pressure from two ,to four minutes.

Plywood when taken from the press after being prepared by this methodcontains only one to two percent. more moisture than before thepressing, while plywood manufactured in accordance with the wet glueprocess contains a much greater per cent. of moisture than when theplies are pressed.

In carrying out our method we may omit the sugar syrup. When sugar syrupis not used, any compound which will make the sheets flexible may beused, such for example as glycerin. If glycerin is used, one to fiveparts by weight is added to the mixture prepared as described above.Plywood man ufactured with glue in which glycerin instead of syrup hasbeen used must 'be made with moist cauls. This moisture may be furnishedto the oauls in any of the usual well known ways and in such quantity asexperience may dictate.

While we havestated above that the glue carrying sheet may be a thinplfy of wood, a sheet of paper, or a sheet of abric, it is obvious thatother materials may be used. The requisites of this carrying part are anability to absorb and carry the glue and a lack of rigidity. This lackof rigidity is quite essential in that it insures that anyirregularities of the sheet will be impotent to produce irregularitiesin the lywood surface. When the sheet is absor nt, we find it best tothoroughly impregnate the sheet with the glue although the surplus gluemay be carried on the-surface. What is really necessary is theprovisionof such a quantity of glue that on heating suificient glue will remainon the exterior of the sheet to properly unite with the ply.

The glue carrying sheets may be used where they are produced. Often,however, it may be found advisableto store themand in such cases it isconvenient to roll the sheet. By using sugar syrup, glycerin, or otherwater carrying materlal in our glue, we insure that our glue shall notbecome brittle and will not crack or chip when the sheet is rolled.

Throughout the above specification we have described in detail theembodiment of our invention which we now prefer. We consider as part ofour invention all changes and modifications which are within the scopeof the appended claims.

, What we claim is:

1, The method of making thin, flexible plywood which consists inimpregnating a glue carrier, such as a thin ply of wood, a sheet ofpaper, a sheet of fabric or similar material with glue composed ofalbumin,

water and a sugar syrup whereby said carrier is rendered flexible andcapable of being rolled into cylinders for convenience in storing ortransporting, drying said carrier, placing said glue carrier between twoor more thin plies of wood and subjecting said plies and said gluecarrier to heat and pressure.

2. The method of making thin, flexible plywood which consists inimpregnatin a glue carrier, such as a thin ply of woo a sheet of paper,a sheet of fabric or similar material with glue composed ofapproximately twenty parts by weight of blood albumin, thirty to eightyparts by weight of water, and fifteen to forty parts by weight of asugar syrup, whereby saidcarrier is rendered flexible and capable ofbeing rolled into cylinders for convenience in storing or transporting,drying said carrier, placing said glue carrier between two or more thinplies of wood and subjecting said plies and said glue carrier to heatand pressure.

3. The method of making thin, flexible plywood which consists invimpregnatin a glue carrier, such as a thin ply of w a sheet of paper, asheet of fabric or similar material with glue composed of albumin, waterand a sugar syrup whereby said carrier is rendered flexible and capableof being rolled into cylinders for convenience in-storing ortransporting, drying said carrier, placing said glue carrier between twoor more thin plies of wood and subjecting said plies and said gluecarrier to approximately one hundred pounds pressure per square inch ata temperature of approximately two hundred and ten degrees Fahrenheit.

In testimony whereof we have hereunto aflixed our signatures.

OLE-NUS L. SPON'SLER. MATTHEW E. DUNLAP. SHERBURNE B. HENNING.

